Electrode for rechargeable lithium battery, and rechargeable lithium battery including the same

ABSTRACT

An electrode for a rechargeable lithium battery includes a current collector and an active material layer on the current collector, wherein the active material layer includes flake-shaped polyethylene particles, and the flake-shaped polyethylene particles have an average particle size (D50) of about 1 μm to about 8 μm. A rechargeable lithium battery includes the electrode including the flake-shaped polyethylene particles.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korean PatentApplication No. 10-2018-0077139 filed in the Korean IntellectualProperty Office on Jul. 3, 2018, the entire content of which isincorporated herein by reference.

BACKGROUND 1. Field

An electrode for a rechargeable lithium battery and a rechargeablelithium battery including the same are disclosed.

2. Description of the Related Art

A portable information device such as a cell phone, a laptop, smartphone, and the like, or an electric vehicle, has used a rechargeablelithium battery having high energy density and easy portability as adriving power source. In addition, research on use of a rechargeablelithium battery as a power source for a hybrid or electric vehicle, oras a power storage device, by using high energy density characteristicshas been actively conducted.

One of the main research tasks of such a rechargeable lithium battery isto improve the safety of the rechargeable battery. For example, if therechargeable lithium battery is exothermic due to internal shortcircuit, overcharge and overdischarge, and/or the like, an electrolytedecomposition reaction and thermal runaway phenomenon may occur. As aresult, an internal pressure inside the battery may rise rapidly tocause battery explosion. Among these, when the internal short circuit ofthe rechargeable lithium battery occurs, there is a high risk ofexplosion because the large amount of electrical energy stored in thebattery is conducted between the shorted positive electrode and negativeelectrode.

SUMMARY

Embodiments of the present disclosure are directed toward featurescapable of improving stability of a rechargeable lithium battery. Anembodiment provides an electrode for a rechargeable lithium batteryhaving improved stability.

Another embodiment provides a rechargeable lithium battery including theelectrode.

According to an embodiment, an electrode for a rechargeable lithiumbattery includes a current collector and an active material layer on thecurrent collector, wherein the active material layer includesflake-shaped polyethylene particles, and the flake-shaped polyethyleneparticles have an average particle size (D50) of about 1 μm to about 8μm.

The flake-shaped polyethylene particles may have an average particlesize (D50) of about 2 μm to about 6 μm.

The flake-shaped polyethylene particles may have a ratio of a major axislength to a minor axis length in a range from about 1 to about 5.

The flake-shaped polyethylene particles may have a thickness of about0.2 μm to about 4 μm.

The active material layer may include an active material and may furtherinclude at least one selected from a conductive material and a binder.

The flake-shaped polyethylene particles may be included in an amount ofabout 0.1 wt % to about 5 wt % based on a total weight of the activematerial layer.

The active material layer may further include a coating layer and theflake-shaped polyethylene particles may be included in at least oneselected from the active material layer and the coating layer.

The flake-shaped polyethylene particles may be included in the coatinglayer.

The coating layer may further include inorganic particles and a binder.

A weight ratio of the sum of the flake-shaped polyethylene particles andthe inorganic particles to the binder may be about 80:20 to about 99:1.

A weight ratio of the flake-shaped polyethylene particles to theinorganic particles may be about 95:5 to about 10:90.

According to another embodiment, a rechargeable lithium batteryincluding the aforementioned electrode for a rechargeable lithiumbattery is provided.

As the reaction rate according to the temperature is improved, an earlyshutdown function may be realized and stability of the rechargeablelithium battery may be secured.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, together with the specification, illustrateembodiments of the subject matter of the present disclosure, and,together with the description, serve to explain principles ofembodiments of the subject matter of the present disclosure.

FIG. 1 is a schematic view of a structure of a rechargeable lithiumbattery according to an embodiment of the present disclosure.

FIG. 2 is an SEM image of spherical-shaped polyethylene particles inwater dispersion state.

FIG. 3 is an SEM image of polyethylene particles according to anembodiment.

FIG. 4 is an SEM image of the active material layer according to anembodiment.

FIG. 5 is a graph showing particle size distributions of respectiveflake-shaped polyethylene particles included in the electrode accordingto Examples 1 to 3.

FIG. 6 is a graph showing resistance increase rates of the electrodeplates of Examples 1 to 3 and the Comparative Example in accordance witha temperature.

FIG. 7 is a graph showing capacity retention after 150 cycles forrechargeable lithium battery cells according to Examples 1 to 3.

FIG. 8 is a schematic view of a coin symmetric cell manufactured toevaluate resistance increase rates of the electrode plates.

DETAILED DESCRIPTION

Hereinafter, referring to the drawings, embodiments of the presentdisclosure are described in more detail. In the following description,functions or constructions not described may be any suitable onesgenerally used in the art.

In order to clearly illustrate and describe the subject matter of thepresent disclosure, the description and relationships of certainfeatures may be omitted. Throughout the disclosure, the same or similarconfiguration elements are designated by the same reference numerals.Also, because the size and thickness of each configuration shown in thedrawing may be arbitrarily shown for better understanding and ease ofdescription, the present disclosure is not necessarily limited thereto.

An electrode for a rechargeable lithium battery according to anembodiment of the present disclosure includes a current collector and anactive material layer on the current collector, wherein the activematerial layer includes flake-shaped polyethylene particles.

The polyethylene particles according to embodiments of the presentdisclosure have a flake-shape as shown in FIG. 3 , and have a differentshape from spherical-shaped polyethylene particles in a water dispersionstate as shown in FIG. 2 . An average particle size of the flake-shapedpolyethylene particles may be defined to be D50.

For example, as shown in FIG. 4 , the flake-shaped polyethyleneparticles have a thin and wide shape on pores in the active materiallayer according to an example embodiment, so the flake-shapedpolyethylene particles are configured to be melted more rapidly (ascompared to the spherical-shaped polyethylene particles) in the event ofa thermal runaway (due to, for example, thermal/physical impacts to arechargeable lithium battery including the electrode) to suppress orreduce the availability and/or functional capabilities of the ionchannels, and they suppress, reduce, or halt the thermal runaway.

In general, polyethylene may be classified, according to the density ofthe polyethylene, into a high density polyethylene (HDPE) having adensity of about 0.94 g/cc to about 0.965 g/cc, a medium densitypolyethylene (MDPE) having a density of about 0.925 g/cc to about 0.94g/cc, a low density polyethylene (LDPE) having a density of about 0.91g/cc to about 0.925 g/cc), or a very low density polyethylene (VLDPE)having a density of about 0.85 g/cc to about 0.91 g/cc.

The flake-shaped polyethylene particles may include for examplepolyethylene polymers such as HDPE, MDPE, and/or LDPE alone or in amixture of two or more.

In the case of including the flake-shaped polyethylene particles, areaction rate according to the temperature is increased under the same(or substantially the same) reaction conditions as compared with thecase of including spherical-shaped polyethylene particles, and thus, astability improvement effect of the rechargeable lithium battery may befurther improved by including the flake-shaped polyethylene particles.For example, when the flake-shaped polyethylene particles are included,an area covering the surfaces of the electrode plate is thinner andwider, before melting, than is the case for the spherical-shapedpolyethylene particles, before melting. If the polyethylene particlesare melted at a temperature exceeding a set or certain temperature andion channels are closed, an electrode plate area where the flake-shapedpolyethylene particles are melted and closed is larger than an electrodeplate area where the spherical-shaped polyethylene particles are meltedand closed, and thus, the flake-shaped polyethylene particles may have afast reaction rate as compared to the spherical-shaped polyethyleneparticles.

For example, during thermal runaway of a battery, the polyethyleneparticles are melted and the ion channel is closed, thereby limitingmovement of ions through the ion channels and resulting in a shutdownfunction. Thus, additional electrical chemical reactions may beprevented or reduced by the shutdown function.

The flake-shaped polyethylene particles may have an average particlesize (D50) of about 1 μm to about 8 μm, and, for example, about 2 μm toabout 6 μm.

As used herein, when a definition is not otherwise provided, averageparticle size (D50) may be measured by any suitable method generallyused in the art such as, for example, by utilizing a particle sizeanalyzer, or transmission electron microscope (TEM) or scanning electronmicroscope (SEM) images (e.g., photographs). In some embodiments, adynamic light-scattering measurement device may be used to perform adata analysis, and the number of particles may be counted for eachparticle size range. From this, the D50 value may be easily obtainedthrough a calculation. For example, the D50 value may correspond to aparticle size at which half of the mass (or volume) of the particleshave a larger particle size and the other half of the mass (or volume)of the particles have a smaller particle size.

On the other hand, the flake-shaped polyethylene particles may have aratio of a major axis length to a minor axis length ranging from about 1to about 5, and specifically from about 1.1 to about 4.5 or from about1.2 to about 3.5.

In addition, the flake-shaped polyethylene particles may have athickness of about 0.2 μm to about 4 μm, and, for example, about 0.3 μmto about 2.5 μm, or about 0.3 μm to about 1.5 μm.

When the flake-shaped polyethylene particles have a size and/orthickness within the ranges described herein, ion channels may beeffectively closed in a small amount (e.g., may be effectively closedrapidly or in a small amount of time).

The active material layer may include an active material and may furtherinclude at least one selected from a conductive material and a binder.

The flake-shaped polyethylene particles may be included in an amount ofabout 0.1 wt % to about 5 wt %, and, for example, about 0.2 wt % toabout 3.0 wt % based on a total weight of the active material layer.

When the amount of the flake-shaped polyethylene particles are withinthe ranges described herein, cycle-life characteristics and outputcharacteristics of a battery may be secured.

The electrode may further include a coating layer, and the flake-shapedpolyethylene particles may be included in at least one selected from theactive material layer and the coating layer.

For example, the flake-shaped polyethylene particles may be included inthe coating layer.

When the flake-shaped polyethylene particles are included in the coatinglayer, the active material layer may be for example a negative activematerial layer.

The coating layer may further include inorganic particles and a binder.

A weight ratio of the sum of the flake-shaped polyethylene particles andthe inorganic particles to the binder may be about 80:20 to about 99:1,and, for example, about 85:15 to about 97:3.

A weight ratio of the flake-shaped polyethylene particles to theinorganic particles may be about 95:5 to about 10:90, and, for example,about 30:70 to about 70:30.

The inorganic particles may include, for example, Al₂O₃, SiO₂, TiO₂,SnO₂, CeO₂, MgO, NiO, CaO, GaO, ZnO, ZrO₂, Y₂O₃, SrTiO₃, BaTiO₃,Mg(OH)₂, boehmite, or a combination thereof, but the present disclosureis not limited thereto. Organic particles such as an acrylic compound,an imide compound, an amide compound, or a combination thereof may befurther included in addition to the inorganic particles, but the presentdisclosure is not limited thereto.

The inorganic particles may be spherical, flake-shaped, cubic, oramorphous. The inorganic particles may have an average particle diameter(e.g., D50) of about 1 nm to about 2500 nm, for example, about 100 nm toabout 2000 nm, or about 200 nm to about 1000 nm, or about 300 nm toabout 800 nm.

In some embodiments, the electrode for a rechargeable lithium batteryaccording to the present disclosure may be a positive electrodeincluding a positive electrode current collector and a positive activematerial layer or a negative electrode including a negative electrodecurrent collector and a negative active material layer.

The positive electrode according to an embodiment of the presentdisclosure includes a positive electrode current collector and apositive active material layer on the positive electrode currentcollector.

The positive electrode current collector may be aluminum or nickel, butthe present disclosure is not limited thereto.

The positive active material may include lithiated intercalationcompounds that reversibly intercalate and deintercalate lithium ions.

For example, the positive active material may include one or morecomposite oxides of lithium and a metal selected from cobalt, manganese,nickel, and a combination thereof.

Examples of the positive active material may include a compoundrepresented by one of the following chemical formulae.

Li_(a)A_(1-b)X_(b)D₂ (0.90≤a≤1.8, 0≤b≤0.5);Li_(a)A_(1-b)X_(b)O_(2-c)D_(c) (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05);Li_(a)E_(1-b)X_(b)O_(2-c)D_(c) (0.90≤a≤1.8, 0≤b≤0.5, 0≤c 0.05);Li_(a)E_(2-b)X_(b)O_(4-c)D_(c) (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05);Li_(a)Ni_(1-b-c)Co_(b)X_(c)D_(α) (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.5, 0<α≤2);Li_(a)Ni_(1-b-c)Co_(b)X_(c)O_(2-α)T_(α) (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05,0<α<2); Li_(a)Ni_(1-b-c)CO_(b)X_(c)O_(2-α)T₂ (0.90≤a≤1.8, 0≤b≤0.5,0≤c≤0.05, 0<α<2); Li_(a)Ni_(1-b-c)Mn_(b)X_(c)D_(α) (0.90≤a≤1.8, 0≤b≤0.5,0≤c≤0.05, 0<α≤2); Li_(a)Ni_(1-b-c)Mn_(b)X_(c)O_(2-α)T_(α) (0.90≤a≤1.8,0≤b≤0.5, 0≤c≤0.05, 0<α<2); Li_(a)Ni_(1-b-c)Mn_(b)X_(c)O_(2-α)T₂(0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, 0<α<2); Li_(a)Ni_(b)E_(c)G_(d)O₂(0.90≤a≤1.8, 0≤b≤0.9, 0≤c≤0.5, 0.001≤d≤0.1);Li_(a)Ni_(b)Co_(c)Mn_(d)G_(e)O₂ (0.90≤a≤1.8, 0≤b≤0.9, 0≤c≤0.5, 0≤d≤0.5,0.001≤e≤0.1); Li_(a)NiG_(b)O₂ (0.90≤a≤1.8, 0.001≤b≤0.1); Li_(a)CoG_(b)O₂(0.90≤a≤1.8, 0.001≤b≤0.1); Li_(a)Mn_(1-b)G_(b)O₂ (0.90≤a≤1.8,0.001≤b≤0.1); Li_(a)Mn₂G_(b)O₄ (0.90≤a≤1.8, 0.001≤b≤0.1);Li_(a)Mn_(1-g)G_(g)PO₄ (0.90≤a≤1.8, 0≤g≤0.5); QO₂; QS₂; LiQS₂; V₂O₅;LiV₂O₅; LiZO₂; LiNiVO₄; Li_((3-f))J₂(PO₄)₃ (0≤f≤2); Li_((3-f))Fe₂(PO₄)₃(0≤f≤2); Li_(a)FePO₄ (0.90≤a≤1.8)

In the foregoing chemical formulae, A is selected from Ni, Co, Mn, and acombination thereof; X is selected from Al, Ni, Co, Mn, Cr, Fe, Mg, Sr,V, a rare earth element, and a combination thereof; D is selected fromO, F, S, P, and a combination thereof; E is selected from Co, Mn, and acombination thereof; T is selected from F, S, P, and a combinationthereof; G is selected from Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, and acombination thereof; Q is selected from Ti, Mo, Mn, and a combinationthereof; Z is selected from Cr, V, Fe, Sc, Y, and a combination thereof;and J is selected from V, Cr, Mn, Co, Ni, Cu, and a combination thereof.

The foregoing compounds may have a coating layer on the surface, or maybe mixed with another compound having a coating layer. The coating layermay include at least one coating element compound selected from an oxideof the coating element, a hydroxide of the coating element, anoxyhydroxide of the coating element, an oxycarbonate of the coatingelement, and a hydroxy carbonate of the coating element. The compoundfor the coating layer may be amorphous or crystalline. The coatingelement included in the coating layer may include Mg, Al, Co, K, Na, Ca,Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or a mixture thereof. The coatinglayer may be formed utilizing a method having no adverse influence (orsubstantially no adverse influence) on properties of a positive activematerial by using these elements in the compound. For example, themethod may include any suitable coating method (e.g., spray coating,dipping, etc.), including those generally used in the art.

The positive active material may be included in an amount of about 90 wt% to about 98 wt % based on a total weight of the positive activematerial layer.

The positive active material layer may further include, optionally, apositive electrode conductive material and a positive electrode binder.

Each amount of the positive electrode conductive material and thepositive electrode binder may be about 1 wt % to about 5 wt % based on atotal weight of the positive active material layer.

The positive electrode conductive material is included to provide apositive electrode with conductivity (e.g., electrical conductivity).Any suitable electronically conductive material may be used as aconductive material unless it causes a chemical change in a battery(e.g., an undesirable change to any of the components of therechargeable lithium battery). Examples thereof may include acarbon-based material such as natural graphite, artificial graphite,carbon black, acetylene black, ketjen black, carbon fiber, and the like;a metal-based material of a metal powder or a metal fiber includingcopper, nickel, aluminum silver, and the like; a conductive polymer suchas a polyphenylene derivative; or a mixture thereof.

The positive electrode binder improves binding properties of positiveactive material particles with one another and with a current collector.Examples thereof may include polyvinyl alcohol, carboxylmethylcellulose, hydroxypropyl cellulose, diacetyl cellulose,polyvinylchloride, carboxylated polyvinylchloride, polyvinylfluoride, anethylene oxide-containing polymer, polyvinylpyrrolidone, polyurethane,polytetrafluoroethylene, polyvinylidene fluoride, polyethylene,polypropylene, a styrene-butadiene rubber, an acrylatedstyrene-butadiene rubber, an epoxy resin, nylon, and the like, but thepresent disclosure is not limited thereto.

In addition, the negative electrode according to another embodiment ofthe present disclosure may include a negative electrode currentcollector and a negative active material layer on the negative electrodecurrent collector.

The negative electrode current collector may include one selected from acopper foil, a nickel foil, a stainless steel foil, a titanium foil, anickel foam, a copper foam, a polymer substrate coated with a conductivemetal, and a combination thereof.

The negative active material may include a material that reversiblyintercalates/deintercalates lithium ions, a lithium metal, a lithiummetal alloy, a material capable of doping/dedoping lithium, and/ortransition metal oxide.

The material that reversibly intercalates/deintercalates lithium ionsmay include any suitable carbon material that is generally used in theart as a carbon-based negative active material in a rechargeable lithiumbattery. Examples of the carbon-based negative active material may becrystalline carbon, amorphous carbon, or a mixture thereof. Thecrystalline carbon may be non-shaped, sheet-shaped, flake-shaped,spherical-shaped, or fiber-shaped natural graphite or artificialgraphite. The amorphous carbon may be a soft carbon, a hard carbon, amesophase pitch carbonization product, fired coke, and/or the like.

The lithium metal alloy includes an alloy of lithium and a metalselected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba,Ra, Ge, Al, and Sn.

The material capable of doping/dedoping lithium may be a silicon-basedmaterial, for example, Si, SiO_(x) (0<x<2), a Si-Q alloy (wherein Q isan element selected from an alkali metal, an alkaline-earth metal, aGroup 13 element, a Group 14 element, a Group 15 element, a Group 16element, a transition metal, a rare earth element, and a combinationthereof, and not Si), a Si-carbon composite, Sn, SnO₂, a Sn—R alloy(wherein R is an element selected from an alkali metal, analkaline-earth metal, a Group 13 element, a Group 14 element, a Group 15element, a Group 16 element, a transition metal, a rare earth element,and a combination thereof, and not Sn), a Sn-carbon composite, and/orthe like. At least one of the foregoing materials may be mixed withSiO₂. The elements Q and R may be selected from Mg, Ca, Sr, Ba, Ra, Sc,Y, Ti, Zr, Hf, Rf, V, Nb, Ta, db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru,Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ge, P,As, Sb, Bi, S, Se, Te, Po, and a combination thereof.

The transition metal oxide may include lithium titanium oxide.

In the negative active material layer, the negative active material maybe included in an amount of about 95 wt % to about 99 wt % based on thetotal weight of the negative active material layer.

The negative active material layer may further include, optionally, anegative electrode conductive material and a negative electrode binder.

Each amount of the negative electrode conductive material and negativeelectrode binder may be about 1 wt % to about 5 wt % based on a totalweight of the negative active material layer.

The negative electrode conductive material may provide negativeelectrode with electrical conductivity. The negative electrodeconductive material may be the same as described herein with respect tothe aforementioned positive electrode conductive material.

The negative electrode binder acts to adhere negative active materialparticles to each other and to adhere the negative active material tothe current collector. The negative electrode binder may be anon-aqueous binder, an aqueous binder, an amphiphilic binder(aqueous/non-aqueous binder), or a combination thereof.

The non-aqueous binder may be polyvinylchloride, carboxylatedpolyvinylchloride, polyvinylfluoride, an ethylene oxide-containingpolymer, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene,polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide,polyimide, or a combination thereof.

The aqueous binder may be a styrene-butadiene rubber, an acrylatedstyrene-butadiene rubber, polyvinyl alcohol, sodium polyacrylate, acopolymer of propylene and a C2 to C8 olefin, a copolymer of(meth)acrylic acid and (meth)acrylic acid alkyl ester, or a combinationthereof.

The amphiphilic binder may be an acrylated styrene-based rubber, and/orthe like.

When the negative electrode binder is an aqueous binder, acellulose-based compound may be further used to provide viscosity as athickener. The cellulose-based compound may include one or more ofcarboxylmethyl cellulose, hydroxypropylmethyl cellulose, methylcellulose, or alkali metal salts thereof. The alkali metals may be Na,K, and/or Li. The thickener may be included in an amount of about 0.1 toabout 3 parts by weight based on 100 parts by weight of the negativeactive material.

Hereinafter, a rechargeable lithium battery according to anotherembodiment of the present disclosure is described with reference to FIG.1 . FIG. 1 is a schematic view of the structure of a rechargeablelithium battery according to an embodiment.

Referring to FIG. 1 , a rechargeable lithium battery 100 according to anembodiment includes a battery cell including a negative electrode 112, apositive electrode 114 facing the negative electrode 112, a separator113 interposed between the negative electrode 112 and the positiveelectrode 114, and an electrolyte for a rechargeable lithium batteryimpregnating the negative electrode 112, the positive electrode 114, andthe separator 113. A battery case 120 houses the battery cell, and asealing member 140 seals the battery case 120.

In some embodiments, a lithium salt is included in the electrolyte andis dissolved in a solvent to act as a source of lithium ions in abattery in order to enable the operation of the basic rechargeablelithium battery and to promote transportation of lithium ion between thepositive electrode and the negative electrode

The lithium salt may include LiPF₆, LiSbF₆, LiAsF₆, LiN(SO₂C₂F₅)₂,Li(CF₃SO₂)₂N, LiN(SO₃C₂F₅)₂, LiC₄F₉SO₃, LiClO₄, LiAlO₂, LiAlCl₄,LiN(C_(x)F_(2x+1)SO₂)(C_(y)F_(2y+2)SO₂) (wherein, x and y are naturalnumbers, for example an integer ranging from 1 to 20), LiCl, Lil,LiB(C₂O₄)₂ (lithium bis(oxalato) borate, LiBOB), or a combinationthereof.

A concentration of the lithium salt may be about 0.1 M to about 2.0 M.When the lithium salt is included at the above concentration range, anelectrolyte may have excellent performance and lithium ion mobility dueto improved or optimal electrolyte conductivity and viscosity.

In some embodiments, the electrolyte may further include an organicsolvent to dissolve the lithium salt. The organic solvent may be anon-aqueous organic solvent having high ion conductivity, a highdielectric constant, and a low viscosity. The non-aqueous organicsolvent serves as a medium for transporting ions taking part in theelectrochemical reaction of a battery.

Such a non-aqueous organic solvent may be, for example, acarbonate-based, ester-based, ether-based, ketone-based, alcohol-based,and/or aprotic solvent.

The carbonate-based solvent may include dimethyl carbonate (DMC),diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropylcarbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate(MEC), ethylene carbonate (EC), propylene carbonate (PC), butylenecarbonate (BC), and/or the like. The ester-based solvent may includemethyl acetate, ethyl acetate, n-propyl acetate, dimethylacetate, methylpropionate, ethyl propionate, propyl propionate, y-butyrolactone,decanolide, valerolactone, mevalonolactone, caprolactone, and/or thelike

The ether-based solvent may include dibutyl ether, tetraglyme, diglyme,dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, and/or thelike, and the ketone-based solvent may be cyclohexanone, and/or thelike.

The alcohol based solvent may include ethanol, isopropyl alcohol, and/orthe like, and the aprotic solvent may include nitriles such as T-CN(wherein T is a C2 to C20 linear, branched, or cyclic hydrocarbon group,a double bond, an aromatic ring, or an ether bond), and/or the like,amides such as dimethyl formamide, and/or the like, dioxolanes such as1,3-dioxolane, and/or the like, sulfolanes, and/or the like.

The non-aqueous organic solvent may be used alone or in a mixture. Whenthe organic solvent is used in a mixture, the mixture ratio may becontrolled in accordance with a desirable battery performance.

The carbonate-based solvent is prepared by mixing a cyclic carbonate anda chain-type carbonate. In this case, when the cyclic carbonate and thechain-type carbonate are mixed together to a volume ratio of about 1:1to about 1:9, performance of an electrolyte may be enhanced.

The non-aqueous organic solvent may further include an aromatichydrocarbon-based organic solvent in addition to the carbonate-basedsolvent. Herein, the carbonate-based solvent and the aromatichydrocarbon-based organic solvent may be mixed to a volume ratio ofabout 1:1 to about 30:1.

The aromatic hydrocarbon-based organic solvent may be an aromatichydrocarbon-based compound of Chemical Formula 1.

In Chemical Formula 1, R₃ to R₈ are the same or different and areselected from hydrogen, a halogen, a C1 to C10 alkyl group, a haloalkylgroup, and a combination thereof.

Examples of the aromatic hydrocarbon-based organic solvent may beselected from benzene, fluorobenzene, 1,2-difluorobenzene,1,3-difluorobenzene, 1,4-difluorobenzene, 1,2,3-trifluorobenzene,1,2,4-trifluorobenzene, chlorobenzene, 1,2-dichlorobenzene,1,3-dichlorobenzene, 1,4-dichlorobenzene, 1,2,3-trichlorobenzene,1,2,4-trichlorobenzene, iodobenzene, 1,2-diiodobenzene,1,3-diiodobenzene, 1,4-diiodobenzene, 1,2,3-triiodobenzene,1,2,4-triiodobenzene, toluene, fluorotoluene, 2,3-difluorotoluene,2,4-difluorotoluene, 2,5-difluorotoluene, 2,3,4-trifluorotoluene,2,3,5-trifluorotoluene, chlorotoluene, 2,3-dichlorotoluene,2,4-dichlorotoluene, 2,5-dichlorotoluene, 2,3,4-trichlorotoluene,2,3,5-trichlorotoluene, iodotoluene, 2,3-diiodotoluene,2,4-diiodotoluene, 2,5-diiodotoluene, 2,3,4-triiodotoluene,2,3,5-triiodotoluene, xylene, and a combination thereof.

As described herein above, the separator 113 may be between the positiveelectrode 114 and the negative electrode 112. The separator 113 mayinclude polyethylene, polypropylene, polyvinylidene fluoride, or amulti-layer thereof and may be a mixed multilayer such as apolyethylene/polypropylene double-layered separator, apolyethylene/polypropylene/polyethylene triple-layered separator, apolypropylene/polyethylene/polypropylene triple-layered separator, orthe like.

Hereinafter, the above aspects of the present disclosure are illustratedin more detail with reference to examples. However, these examples areexemplary, and the present disclosure is not limited thereto.

Manufacture of Rechargeable Lithium Battery Cell

Example 1 Battery Cell Including Flake-Shaped 2 μm PE Particles

95 wt % of a positive active material in which LiCoO₂/LiFePO₄“LCO/LFP”were mixed to a weight ratio of 9:1, 3 wt % of a polyvinylidene fluoridebinder, and 2 wt % of a ketjen black conductive material were mixed in aN-methyl pyrrolidone solvent to provide a positive active materialslurry. The positive active material slurry was coated on both surfacesof an aluminum current collector, dried and compressed to provide apositive electrode formed with a positive active material layer.

98 wt % of graphite, 0.8 wt % of carboxylmethyl cellulose, and 1.2 wt %of styrene-butadiene rubber were mixed in pure water to provide anegative active material slurry. The negative active material slurry wascoated on both surfaces of a copper current collector, dried, andcompressed to provide a negative electrode formed with a negative activematerial layer.

48 wt % of flake-shaped polyethylene (PE) particles having an averageparticle size of 2 μm (major axis length/minor axis length ratio=about2, thickness=about 0.6 μm, D50=2 μm), 47 wt % of alumina (averageparticle diameter (D50)=0.7 μm), and 5 wt % of an acrylatedstyrene-based rubber binder were mixed in an alcohol-based solvent toprovide a PE/alumina slurry.

The PE/alumina slurry was coated on both surfaces of the negativeelectrode, dried, and compressed to provide a negative electrode formedwith a coating layer including flake-shaped PE particles.

The positive electrode, a separator including a PE/polypropylene (PP)multi-layer substrate, the negative electrode formed with the coatinglayer including the flake-shaped PE particles were sequentially stackedto provide an electrode assembly having a structure shown in FIG. 1 ,and then an electrolyte (1.0 M LiPF₆ in EC/DEC=50:50 v/v) was injectedto provide a rechargeable battery cell.

Example 2 Battery Cell Including Flake-Shaped 4 μm PE Particles

A rechargeable battery cell was manufactured in accordance withsubstantially the same procedure as in Example 1, except that thenegative electrode was prepared using flake-shaped PE particles havingan average particle size of 4 μm (major axis length/minor axis lengthratio=about 2.4, thickness=about 0.6 μm, D50=4 μm).

Example 3 Battery Cell Including Flake-Shaped 6 μm PE Particles

A rechargeable battery cell was manufactured in accordance with the sameprocedure as in Example 1, except that the negative electrode wasprepared using flake-shaped PE particles having an average particle sizeof 6 μm (major axis length/minor axis length ratio=about 2.4,thickness=about 0.6 μm, D50=6 μm).

The results of particle distributions of flake-shaped polyethyleneparticles included in the electrode according to Examples 1 to 3 areshown in FIG. 5 .

Comparative Example Battery Cell Including Spherical-Shaped PE Particles

A rechargeable battery cell was manufactured in accordance withsubstantially the same procedure as in Example 1, except that thenegative electrode was prepared using a dispersion in whichspherical-shaped PE particles having an average particle size of 4 μmwere dispersed in an alcohol-based solvent instead of the flake-shapedPE particles having an average particle size of 2 μm.

Evaluation Examples

1. Evaluation of Resistance Increase Rate of Electrode Plate

A negative electrode formed with a coating layer including flake-shapedPE particles according to Example 1, a separator including a PE/PPmulti-layer substrate, and a negative electrode formed with a coatinglayer including flake-shaped PE particles according to Example 1 weresequentially stacked, and an electrolyte including 1M LiBF₄ dissolved inpropylene carbonate was injected thereto to provide a coin symmetriccell shown in FIG. 8 .

FIG. 8 is a schematic view of a coin symmetric cell manufactured toevaluate resistance increase rates of the electrode plates. Referring toFIG. 8 , a coin symmetric cell 200 (which may also be referred to as asymmetrical blocking electrode cell), includes a bottom case 220, aspring 210, a negative electrode 212, a first spacer 216, a separator218, a second spacer 222, a positive electrode 214, and a top case 224,stacked in the stated order. The spring 210 included 3 springs, thenegative electrode 212 had a diameter of 15.5 mm φ, the first spacer 216and the second spacer 222 each had a thickness of 500 μm, and theseparator 218 included a polyethylene (PE) separator having a diameterof 19 mm φ (612HS). The coin symmetric cell 200 was impregnated with anelectrolyte (EL) including 50 μL of 1M LiBF₄ in propylene carbonate(PC).

The obtained coin symmetric cell was introduced into a temperaturechangeable chamber after mounting a temperature sensor and a resistancemeasurer (a resistance meter) and evaluated. Changes in temperature andresistance of the coin symmetric cell were measured while increasing thetemperature at a rate of 10° C./minute, and the results of evaluatingthe resistance increase rate of an electrode plate according to atemperature are shown in FIG. 6 .

FIG. 6 is a graph showing resistance increase rates of the electrodeplates in accordance with a temperature.

Referring to FIG. 6 , it can be seen that the resistance increase rateof the electrode plate according to the Examples (e.g., Examples 1 to 3)was significantly higher than the Comparative Example at a hightemperature of 120° C. or higher.

From this, it can be seen that in a case of a battery cell including anelectrode according to an embodiment, ion channels are effectivelysuppressed (or the availability and/or functionality of the ion channelsmay be reduced) during thermal runaway by the thermal/physical impact,so the shut-down function may be expressed or initiated at an earlystage.

2. Evaluation of Cycle-Life Characteristics

Rechargeable lithium battery cells obtained from Examples 1 to 3 werecharged at a rate of 0.5 C/0.5 C and at 4.4 V and then discharged until3.0 V, and the cell capacity decrease rate after 150 cycles wasmeasured. The results thereof are shown in FIG. 7 . At 51 cycles and 101cycles, they were charged at a rate of 0.2 C/0.2 C at 4.4 V and thendischarged at 3.0V to evaluate a recovered capacity.

FIG. 7 is a graph showing capacity retention for 150 cycles ofrechargeable lithium battery cells according to Examples 1 to 3.

Referring to FIG. 7 , excellent capacity retention after 150 cycles areexhibited by the battery cells according to Examples 1 to 3.

Resultantly, the rechargeable lithium battery cell according to anembodiment may have effective shut-down functions while maintainingexcellent battery characteristics.

It will be understood that, although the terms “first,” “second,”“third,” etc., may be used herein to describe various elements,components, regions, layers and/or sections, these elements, components,regions, layers and/or sections should not be limited by these terms.These terms are used to distinguish one element, component, region,layer or section from another element, component, region, layer orsection. Thus, a first element, component, region, layer or sectiondescribed below could be termed a second element, component, region,layer or section, without departing from the spirit and scope of thepresent disclosure.

Spatially relative terms, such as “beneath,” “below,” “lower,” “under,”“above,” “upper,” and the like, may be used herein for ease ofexplanation to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. It will beunderstood that the spatially relative terms are intended to encompassdifferent orientations of the device in use or in operation, in additionto the orientation depicted in the figures. For example, if the devicein the figures is turned over, elements described as “below” or“beneath” or “under” other elements or features would then be oriented“above” the other elements or features. Thus, the example terms “below”and “under” can encompass both an orientation of above and below. Thedevice may be otherwise oriented (e.g., rotated 90 degrees or at otherorientations) and the spatially relative descriptors used herein shouldbe interpreted accordingly.

It will be understood that when an element or layer is referred to asbeing “on,” “connected to,” or “coupled to” another element or layer, itcan be directly on, connected to, or coupled to the other element orlayer, or one or more intervening elements or layers may be present. Inaddition, it will also be understood that when an element or layer isreferred to as being “between” two elements or layers, it can be theonly element or layer between the two elements or layers, or one or moreintervening elements or layers may also be present.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the presentdisclosure. As used herein, the singular forms “a” and “an” are intendedto include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the terms“comprises,” “comprising,” “includes,” and “including,” when used inthis specification, specify the presence of the stated features,integers, acts, operations, elements, and/or components, but do notpreclude the presence or addition of one or more other features,integers, acts, operations, elements, components, and/or groups thereof.As used herein, the term “and/or” includes any and all combinations ofone or more of the associated listed items. Expressions such as “atleast one of,” when preceding a list of elements, modify the entire listof elements and do not modify the individual elements of the list.

As used herein, the terms “substantially,” “about,” and similar termsare used as terms of approximation and not as terms of degree, and areintended to account for the inherent deviations in measured orcalculated values that would be recognized by those of ordinary skill inthe art. Further, the use of “may” when describing embodiments of thepresent disclosure refers to “one or more embodiments of the presentdisclosure.” As used herein, the terms “use,” “using,” and “used” may beconsidered synonymous with the terms “utilize,” “utilizing,” and“utilized,” respectively. Also, the term “exemplary” is intended torefer to an example or illustration.

Also, any numerical range recited herein is intended to include allsub-ranges of the same numerical precision subsumed within the recitedrange. For example, a range of “1.0 to 10.0” is intended to include allsubranges between (and including) the recited minimum value of 1.0 andthe recited maximum value of 10.0, that is, having a minimum value equalto or greater than 1.0 and a maximum value equal to or less than 10.0,such as, for example, 2.4 to 7.6. Any maximum numerical limitationrecited herein is intended to include all lower numerical limitationssubsumed therein, and any minimum numerical limitation recited in thisspecification is intended to include all higher numerical limitationssubsumed therein. Accordingly, Applicant reserves the right to amendthis specification, including the claims, to expressly recite anysub-range subsumed within the ranges expressly recited herein.

Hereinbefore, certain embodiments of the present disclosure have beendescribed and illustrated. It should be apparent to a person havingordinary skill in the art, however, that the subject matter of thepresent disclosure is not limited to the embodiments as describedherein, and may be variously modified and transformed without departingfrom the spirit and scope of the present disclosure. Accordingly, themodified or transformed embodiments as such may not be understoodseparately from the technical ideas and aspects of the presentdisclosure, and the modified embodiments are within the scope of theclaims of the present disclosure, and equivalents thereof.

DESCRIPTION OF AT LEAST SOME OF THE SYMBOLS

-   100: rechargeable lithium battery-   112: negative electrode-   113: separator-   114: positive electrode-   120: battery case-   140: sealing member-   200: coin symmetric cell-   210: spring-   212: negative electrode-   214: positive electrode-   216: first spacer-   218: separator-   220: bottom case-   222: second spacer-   224: top case

What is claimed is:
 1. An electrode for a rechargeable lithium battery,comprising: a current collector, and an active material layer on thecurrent collector, wherein the active material layer comprisesflake-shaped polyethylene particles, the flake-shaped polyethyleneparticles have an average particle size (D50) of 1 μm to 8 μm, and theflake-shaped polyethylene particles have a ratio of a major axis lengthto a minor axis length in a range from 2.4 to 4.5.
 2. The electrode fora rechargeable lithium battery of claim 1, wherein the flake-shapedpolyethylene particles have an average particle size (D50) of 2 μm to 6μm.
 3. The electrode for a rechargeable lithium battery of claim 1,wherein the flake-shaped polyethylene particles have a thickness of 0.3μm to 4 μm.
 4. The electrode for a rechargeable lithium battery of claim1, wherein the active material layer comprises an active material andfurther comprises at least one selected from a conductive material and abinder.
 5. The electrode for a rechargeable lithium battery of claim 4,wherein the flake-shaped polyethylene particles are included in anamount of 0.1 wt % to 5 wt % based on a total weight of the activematerial layer.
 6. The electrode for a rechargeable lithium battery ofclaim 1, wherein the electrode further comprises a coating layer, andthe flake-shaped polyethylene particles are included in at least oneselected from the active material layer and the coating layer.
 7. Theelectrode for a rechargeable lithium battery of claim 6, wherein theflake-shaped polyethylene particles are included in the coating layer.8. The electrode for a rechargeable lithium battery of claim 7, whereinthe coating layer further comprises inorganic particles and a binder. 9.The electrode for a rechargeable lithium battery of claim 8, wherein aweight ratio of the sum of the flake-shaped polyethylene particles andthe inorganic particles to the binder is 80:20 to 99:1.
 10. Theelectrode for a rechargeable lithium battery of claim 8, wherein aweight ratio of the flake-shaped polyethylene particles to the inorganicparticles is 95:5 to 10:90.
 11. A rechargeable lithium batterycomprising the electrode for a rechargeable lithium battery of claim 1.